The floristics and structure of heathland vegetation exhibiting symptoms of Phytophthora cinnamomi Rands infestation was assessed at two sites in heathlands at Anglesea, Victoria. There were significant effects in both floristics and structure. Thirteen heathland species were significantly less abundant in diseased areas and 23 species were more abundant. Diseased (infested) vegetation, when compared with non-diseased areas, had less cover of Xanthorrhoea australis and shrub species and a greater cover of sedges, grasses and open ground. Structural differences were observed between heights 0 and 0.6 m, with a decline in cover recorded in diseased vegetation. Non-metric multidimensional scaling ordination of the floristic data showed a clear separation of diseased and non-diseased vegetation and that changes in floristic composition post-infestation were similar at both sites. Although there was some evidence of regeneration of X. australis, the recovery capacity of other susceptible species at Anglesea is unknown. The long-term consequences of loss of species and structure in the eastern Otways mean that the vegetation is unlikely to return to former status, especially if the pathogen continues to reinfect.
Many hyperaccumulators of nickel (Ni) are endemic to ultramafic soils and always show very high Ni concentrations. Others occur on a variety of substrates but accumulate high Ni from the ultramafic ones. Pimelea leptospermoides is unusual in being an ultramafic endemic that shows a very wide range of Ni concentrations. The present work sought to establish the factors governing the wide variation in Ni uptake by P. leptospermoides, and aimed to investigate the likelihood of this variation originating from plant differences or soil differences. Multiple paired plant and soil samples were taken over the geographic range of occurrence of P. leptospermoides. Plant and soil metal concentrations and soil pH were measured. No evidence was found to suggest that the plants belong to populations with inherent ‘high-Ni’ and ‘low-Ni’ accumulation capability. Instead, the soil pH (covering a range from 6.0 to 8.3) and the total soil Ni concentrations of the ultramafic soils were found to be the major influences on the level of Ni accumulation. The wide variation observed in Ni accumulation by P. leptospermoides from ultramafic soils can be explained by a combination of variations in soil pH and total soil Ni concentrations.
Selecting native plant species with characteristics suitable for extraction of heavy metals may have multiple advantages over non-native plants. Six Australian perennial woody plant species and one willow were grown in a pot trial in heavy metal-contaminated biosolids and a potting mix. The plants were harvested after fourteen months and above-ground parts were analysed for heavy metal concentrations and total metal contents. All native species were capable of growing in biosolids and extracted heavy metals to varying degrees. No single species was able to accumulate heavy metals at particularly high levels and metal extraction depended upon the bioavailability of the metal in the substrate. Metal extraction efficiency was driven by biomass accumulation, with the species extracting the most metals also having the greatest biomass yield. The study demonstrated that Grevillea robusta, Acacia mearnsii, Eucalyptus polybractea, and E. cladocalyx have the greatest potential as phytoextractor species in the remediation of heavy metal-contaminated biosolids. Species survival and growth were the main determinants of metal extraction efficiency and these traits will be important for future screening of native species.
The significant impacts of the introduced plant pathogen Phytophthora cinnamomi on native Australian vegetation have been well documented, but there is less knowledge of long-term effects. We assessed long-term (26 years) disease progression and impacts on vegetation floristics and structure at a heathy woodland site in the Great Otway National Park, eastern section. Disease progressed dramatically between 1989 and 2005 and by 2015 only 0.08% of the site was non-diseased. There were significant declines in plant species richness and numbers of susceptible species; and increases in percentage cover of resistant sedges and grasses overall, and in cover of Leptospermum continentale (prickly tea-tree) in post-disease areas. There were significant declines of Xanthorrhoea australis (Austral grass-tree), a keystone species that contributes greatly to vegetation structure and fauna habitat. There is an urgent need to map the distribution of P. cinnamomi affected vegetation and identify floristically important non-diseased vegetation in the national park. It is imperative that quarantine of non-infested areas, phosphite application, track closures and vehicle wash-downs be implemented to reduce disease extension and protect the significant biodiversity of the region including species rich heathlands and nationally listed threatened plant and fauna species and their habitats.
Biosolids produced by sewage treatment facilities can exceed guideline thresholds for contaminant elements. Phytoextraction is one technique with the potential to reduce these elements allowing reuse of the biosolids as a soil amendment. In this field trial, cuttings of seven species/cultivars of Salix(willows) were planted directly into soil and into biosolids to identify their suitability for decontaminating biosolids. Trees were irrigated and harvested each year for three consecutive years. Harvested biomass was weighed and analyzed for the contaminant elements: As, Cd, Cu, Cr, Hg, Pb, Ni, and Zn. All Salix cultivars, except S. chilensis, growing in soils produced 10 to 20 t ha(-1) of biomass, whereas most Salix cultivars growing in biosolids produced significantly less biomass (<6 t ha(-1)). Salix matsudana (30 t ha(-1)) and S. × reichardtii A. Kerner (18 t ha(-1)) had similar aboveground biomass production in both soil and biosolids. These were also the most successful cultivars in extracting metals from biosolids, driven by superior biomass increases and not high tissue concentrations. The willows were effectual in extracting the most soluble/exchangeable metals (Cd, 0.18; Ni, 0.40; and Zn, 11.66 kg ha(-1)), whereas Cr and Cu were extracted to a lesser degree (0.02 and 0.11 kg ha(-1)). Low bioavailable elements, As, Hg, and Pb, were not detectable in any of the aboveground biomass of the willows.
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